The present invention relates to hydraulic systems in general and more particularly to a hydraulic control apparatus comprising a hydraulic master cylinder and a hydraulic slave cylinder for operating a mechanism remotely located from the master cylinder, the hydraulic control apparatus being prefilled with hydraulic fluid and pretested prior to shipment to a motor vehicle manufacturer, for example, for installation in a motor vehicle.
It is now known to prefill with hydraulic fluid a motor vehicle clutch control apparatus comprising a master cylinder, a reservoir of hydraulic fluid and a slave cylinder for operating a throw out bearing of a mechanical diaphragm spring clutch. Such prefilled hydraulic control apparatus are shown for example in U.S. Pat. Nos. 4,407,125, 4,599,860, 4,503,678, 4,506,507, 4,607,670, 4,624,290 and 4,624,291, all assigned to the assignee of the present application.
As is well known, prefilling with hydraulic fluid and pretesting hydraulic apparatus for operating vehicle mechanisms such as mechanical clutches presents the many advantages, for the motor vehicle manufacturer, of receiving a fully assembled mechanism comprising all of the components filled with hydraulic fluid and pretested for proper operation ready to install on a motor vehicle on the assembly line without requiring that the components be installed separately, connected by way of a flexible conduit, and filled after installation with hydraulic fluid while being purged of any atmospheric air contained in the apparatus.
It is critical to the successful implementation of such prefilled and pretested hydraulic control apparatus that the pretesting of the prefilled unites be carried out in an efficient, effective and inexpensive manner. Whereas various methods and apparatus have been proposed and utilized in the past to test such prefilled hydraulic apparatus prior to delivery to the ultimate user, the prior art methods and apparatus have embodied relatively time consuming processes and have required the utilization of relatively expensive capital equipment.